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Transcript
7.4 Human Genetics and Pedigrees KEY CONCEPT A combination of methods is used to study human genetics. 7.4 Human Genetics and Pedigrees Human genetics follows the patterns seen in other organisms. - phenotype may be influenced by the environment (such as nutrition) 7.4 Human Genetics and Pedigrees * Types of traits 1. single-gene traits = have 1 allele (dominant or recessive) that determines phenotype Ex: widow’s peak (dominant trait), straight hairline (recessive trait) 7.4 Human Genetics and Pedigrees 2. polygenic traits = phenotype based on multiple alleles Ex: eye color 7.4 Human Genetics and Pedigrees * Sex Linked Disorders - only females can be carriers - since females have more than one X chromosome, the normal allele masks the disorder that is located on the other X chromosome - males do not have another X, so they cannot be carriers – if their X carries the disorder, they will have the disorder Ex: hemophilia (was most noted in the family of Queen Victoria) 7.4 Human Genetics and Pedigrees - hemophilia is a rare bleeding disorder Y X - people affected by hemophilia have a deficient protein/factor needed for blood to clot 7.4 Human Genetics and Pedigrees * Pedigree - is a chart that is used to trace the phenotypes and genotypes within a family (this is different from a Punnett square, which is used to determine the probable outcome from a cross) 7.4 Human Genetics and Pedigrees - male = marriage - female = - carrier = - shows phenotype = - when enough family phenotypes are known, genotypes can be inferred 7.4 Human Genetics and Pedigrees * Pedigrees can be used to trace autosomal and sex-linked disorders - looking at a pedigree - if there are about the same number of males and females who have the phenotype, then the gene is most likely on an autosome - if the phenotype is more common in males, then the gene is most likely on a sex chromosome (on the X chromosome – remember, they don’t have a back up!) 7.4 Human Genetics and Pedigrees - genotype can be inferred based on the pattern of inheritance (seeFig. 7.14, p.215) Fig 7.14 -Ex: work your way up…start with the children - if only 2 of the 3 children express the widow’s peak phenotype (#8 and #10) = autosomal dominant; therefore one parent must be heterozygous (#4) and the other must be homozygous recessive (#3) 7.4 Human Genetics and Pedigrees - sex-linked genes can also be traced Ex: colorblindness female carrier x male not colorblind XM Y XM XM XM X MY Xm X M Xm Xm Y carrier daughter X M = dominant Xm = recessive colorblindness is a recessive sexlinked disorder these 2 kids are not affected colorblind son 7.4 Human Genetics and Pedigrees * Karyotype - is used to study human genetics XY 7.4 Human Genetics and Pedigrees ~ is a picture of all the chromosomes in a cell ~ are stained so they can be compared and studied (each chromosome stains differently); are used by scientists to identify: 7.4 Human Genetics and Pedigrees 1. - extra chromosomes 2. - missing chromosomes 3. - chromosome abnormalities 4. - locate a gene 5. - estimate the distances between genes on a chromosome 7.4 Human Genetics and Pedigrees - Down Syndrome (also called Trisomy 21) ~ caused by having an extra chromosome #21 Chris Burke of Life Goes On – he is the first actor with Down’s Syndrome to star on TV 7.4 Human Genetics and Pedigrees Huntington’s Disease - autosomal dominant disorder - caused by a genetic defect on chromosome 4 - symptoms are displayed at around age 30 – 40 - causes nerve cells in parts of the brain break down